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  • 1
    Publication Date: 2011-08-24
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Journal of Aircraft (ISSN 0021-8669); 30; 5; p. 763-768.
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  • 2
    Publication Date: 2011-08-24
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Journal of Aircraft (ISSN 0021-8669); 30; 4; p. 453-458.
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  • 3
    Publication Date: 2011-08-24
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 15; 4, Ju; 878-884
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  • 4
    Publication Date: 2011-08-19
    Description: A scheme for theoretical and experimental evaluation of multivariable system stability robustness measures is described. The experimental scheme is based on the estimation of frequency responses from power-spectra analyses of a set of time responses due to sine-sweep excitation at each input and then computation of the appropriate singular values. The procedure can also be used on an open-loop stable system to predict the closed-loop stability before closing the loop. Classical Nyquist diagrams can also be constructed to determine one-loop-at-a-time gain or phase margins. The scheme has been implemented in a wind tunnel test for singular-value evaluation of digital flutter suppression control laws and compared with theory. The singular values at the plant input and output of the actual system and the theoretical model are qualitatively similar but have some discrepancies.
    Keywords: CYBERNETICS
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  • 5
    Publication Date: 2013-08-31
    Description: The desire to achieve orbit-on-demand access to space with rapid turn-around capability and aircraft-like processing operations has given rise to numerous hypersonic aerospace plane design concepts which would take off horizontally from a conventional runway and employ air-breathing scramjet propulsion systems for acceleration to orbital speeds. Most of these air-breathing hypersonic vehicle concepts incorporate an elongated fuselage forebody to act as the aerodynamic compression surface for a scramjet combustor module. This type of airframe-integrated scramjet propulsion system tends to be highly sensitive to inlet conditions and angle-of-attack perturbations. Furthermore, the basic configuration of the fuselage, with its elongated and tapered forebody, produces relatively low frequency elastic modes which will cause perturbations in the combustor inlet conditions due to the oscillation of the forebody compression surface. The flexibility of the forebody compression surface, together with sensitivity of scramjet propulsion systems to inlet conditions, creates the potential for an unprecedented form of aeroelastic-propulsive interaction in which deflections of the vehicle fuselage give rise to propulsion transients, producing force and moment variations that may adversely impact the longitudinal flight dynamics and/or excite the elastic modes. These propulsive force and moment variations may have an appreciable impact on the performance, guidance, and control of a hypersonic aerospace plane. The objectives of this research are to quantify the magnitudes of propulsive force and moment perturbations resulting from elastic deformation of a representative hypersonic vehicle, and to assess the potential impact of these perturbations on the vehicle's longitudinal flight dynamics.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA LaRC Workshop on Guidance, Navigation, Controls, and Dynamics for Atmospheric Flight, 1993; p 459-472
    Format: application/pdf
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  • 6
    Publication Date: 2013-08-31
    Description: Time-correlated gust loads are time histories of two or more load quantities due to the same disturbance time history. Time correlation provides knowledge of the value (magnitude and sign) of one load when another is maximum. At least two analysis methods have been identified that are capable of computing maximized time-correlated gust loads for linear aircraft. Both methods solve for the unit-energy gust profile (gust velocity as a function of time) that produces the maximum load at a given location on a linear airplane. Time-correlated gust loads are obtained by re-applying this gust profile to the airplane and computing multiple simultaneous load responses. Such time histories are physically realizable and may be applied to aircraft structures. Within the past several years there has been much interest in obtaining a practical analysis method which is capable of solving the analogous problem for nonlinear aircraft. Such an analysis method has been the focus of an international committee of gust loads specialists formed by the U.S. Federal Aviation Administration and was the topic of a panel discussion at the Gust and Buffet Loads session at the 1989 SDM Conference in Mobile, Alabama. The kinds of nonlinearities common on modern transport aircraft are indicated. The Statical Discrete Gust method is capable of being, but so far has not been, applied to nonlinear aircraft. To make the method practical for nonlinear applications, a search procedure is essential. Another method is based on Matched Filter Theory and, in its current form, is applicable to linear systems only. The purpose here is to present the status of an attempt to extend the matched filter approach to nonlinear systems. The extension uses Matched Filter Theory as a starting point and then employs a constrained optimization algorithm to attack the nonlinear problem.
    Keywords: STRUCTURAL MECHANICS
    Type: Research in Structures, Structural Dynamics and Materials, 1990; p 221-229
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  • 7
    Publication Date: 2013-08-31
    Description: Described here is the development and implementation of on-line, near real time controller performance evaluation (CPE) methods capability. Briefly discussed are the structure of data flow, the signal processing methods used to process the data, and the software developed to generate the transfer functions. This methodology is generic in nature and can be used in any type of multi-input/multi-output (MIMO) digital controller application, including digital flight control systems, digitally controlled spacecraft structures, and actively controlled wind tunnel models. Results of applying the CPE methodology to evaluate (in near real time) MIMO digital flutter suppression systems being tested on the Rockwell Active Flexible Wing (AFW) wind tunnel model are presented to demonstrate the CPE capability.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, Part 2; p 615-65
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  • 8
    Publication Date: 2013-08-31
    Description: This work-in-progress presentation describes an ongoing research activity at the NASA Langley Research Center to develop analytical methods for the prediction of aerothermoelastic stability of hypersonic aircraft including active control systems. The objectives of this research include application of aerothermal loads to the structural finite element model, determination of the thermal effects on flutter, and assessment of active controls technology applied to overcome any potential adverse aeroelastic stability or response problems due to aerodynamic heating- namely flutter suppression and ride quality improvement. For this study, a generic hypersonic aircraft configuration was selected which incorporates wing flaps, ailerons and all-moveable fins to be used for active control purposes. The active control systems would use onboard sensors in a feedback loop through the aircraft flight control computers to move the surfaces for improved structural dynamic response as the aircraft encounters atmospheric turbulence.
    Keywords: STRUCTURAL MECHANICS
    Type: Research in Structures, Structural Dynamics and Materials, 1990; p 249-261
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  • 9
    Publication Date: 2011-08-19
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 346-352
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  • 10
    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 605-611
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